Prosthetic intervertebral discs for use in the lumbar spine are a new technology with a short history of clinical use in Europe. They are used as a substitute for chronically injured or ruptured and excised intervertebral disc in the spinal column of the vertebrae for humans. Such devices employ one, two, three or more individual elements having a wide range of constructs including ball and socket joints, gel filled enclosures, spring-biased plates, plate and joint combinations and others. Prosthetic spinal discs have been used and reported about primarily in the lumbar spine.
Known prosthetic spinal discs generally require some form of articulation or inherent flexibility in the device to permit a spine having the device to maintain its natural posture and range of motion as much as possible.
Several patents disclose particular artificial spinal discs comprising two articulating plate members which are affixed to adjacent superior and inferior vertebrae in one fashion or another. Particular modes of articulation of the two plates has generally been used to distinguish the various devices in this field. As vertebrae generally have rounded outer periphery as viewed from a superior to inferior direction, the outer periphery of known artificial spinal discs are generally rounded, circular, oval, or kidney-shaped. Known artificial discs have also been made from a large variety of materials such as plastic, rubber, metal, ceramic and alloys.
Prosthetic spinal discs comprising two plates, each plate having a planar surface attached to an adjacent vertebra, are disclosed in U.S. Pat. Nos. 4,309,777, 4,759,769 and 5,458,642. Prosthetic spinal discs comprising two plates, each plate having a planar first surface attached to an adjacent vertebra and a contoured opposing second surface separated by an interposed core or member that articulates or cooperates with the contoured surfaces of the respective plates, are disclosed in U.S. Pat. Nos. 4,759,766, 5,314,477, 5,556,431 and 5,562,738.
U.S. Pat. No. 5,401,269 to Buttner-Janz et al. discloses an intervertebral disc endoprosthesis generally comprising at least two articulating plates which are rotatable relative to one another about a vertical axis.
U.S. Pat. No. 4,349,921 to Kuntz discloses an intervertebral disc prosthesis comprising a body having a superior surface, an inferior surface, opposing lateral surfaces and opposing anterior and posterior ends, wherein each of the superior and inferior surfaces is "substantially flat in the lateral-lateral direction over the entirety of the surfaces" and "in the anterior-posterior direction corresponding generally with the shape of a vertebral surface adjacent the disc." The intervertebral disc prosthesis further comprises "means for holding the prosthesis" to a vertebra.
U.S. Pat. No. 5,258,031 to Salib et al. discloses an intervertebral disc arthroplasty comprising: 1) a first member having a first joint surface, a first anterior end and an opposing first posterior end, the anterior and posterior ends defining a transverse midline therebetween; 2) a second member having a second joint surface, a second anterior end and an opposing second posterior end; and 3) a ball and socket joint located between the first and second joint surfaces and between the transverse midline and the first posterior end. The ball and socket joints permits relative rotation of the first and second member about a first axis parallel to the transverse midline and about a second axis perpendicular to the first axis.
U.S. Pat. No. 5,425,773 to Boyd et al. discloses an intervertebral disc arthroplasty comprising: 1) a first member having a first joint surface, a first anterior end and an opposing first posterior end, the anterior and posterior ends defining a transverse midline therebetween; 2) a second member having a second joint surface, a second anterior end and an opposing second posterior end; and 3) a ball and socket joint between the fist and second joint surfaces and between the transverse midline and the first posterior end. The ball and socket joints permits relative rotation of the first and second member about a first axis parallel to the transverse midline and about a second axis perpendicular to the first axis. Additionally, at least one of the first and second joint surfaces is inclined away from the ball and socket joint entirely around the joint, and the other one of the first and second joint surfaces lies along a plane substantially parallel to both the first and second axes.
U.S. Pat. No. 5,676,701 to Yuan et al. discloses a low wear artificial spinal disc comprising: 1) a first component including a recess having a contoured surface with a 360.degree. circumference; and 2) a second component including a projection having a contoured surface with a 360.degree. circumference. The contoured surfaces permit unrestricted rotational motion and a flexion/extension bending motion between the components relative to a standing patient's spinal axis. The flexion/extension angle is between about 20.degree.-30.degree..
A human spinal disc can be thought of as a gel filled sac which employs various modes of articulation that provide for changing the instant center of rotation of adjacent vertebral surfaces relative to one another and that permit lateral-to-lateral and anteroposterior translation of vertebrae relative to one another. An artificial spinal disc should be capable of articulating in a fashion similar to a human spinal disc. However, articulation in known spinal disc prostheses comprising two or more articulating components is generally limited to modes wherein the instant center of rotation of the components relative to one another does not change. This absence of a physiological movement in the instant center of rotation with flexion, is responsible for the translation of nonphysiological forces to the adjacent disc surfaces which is believed to accelerate the rate of disc degeneration and the need for subsequent or additional surgical intervention. Accordingly, there exists a need for an artificial spinal disc comprising plural components which disc provides for articulation wherein an instant center of rotation changes and which disc provides for translation of adjacent vertebrae relative to one another.
Known prosthetic spinal discs suffer disadvantages including the movement of the end plates, dislocation of the endplates, polyethylene cold flow, cold-welds of metal on metal components, ossification of the annulus, and particulate wear and debris of the component parts. There remains a need for an artificial disc, which mimics natural spinal segmental motion and provides an improved alternative to spinal fusion. Analogous to the situation with degenerative hips and knees where viable mechanical substitutes exist to enhance function and relieve pain, such a device will relieve pain for patients with end-stage disc disease, promote the preservation of natural motion, and create a device with the durability necessary for long-term use. There remains a need for a prosthetic disc which can mimic natural segmental spinal motion, relieve pain, and provide durability for long-term use.